Swell and darkness hampered boat rescue

High seas and darkness hindered attempts to rescue more than 100 drowning asylum seekers, a Perth court has heard.

Indonesian nationals Boy Djara and Justhen are on trial in the Perth District Court accused of being involved in an ill-fated people smuggling voyage that led to the deaths of 102 people about 200km from Christmas Island in June 2012.

The pair have pleaded not guilty to six charges each of trying to assist illegal non-citizens into Australia.

Their small wooden fishing vessel was packed with 210 male passengers, mostly from Pakistan and Afghanistan, and started taking on water before eventually capsizing.

Two other crew members did not survive.

Despite the incident being in Indonesian waters, Australia took control of the rescue.

Lieutenant Commander Jonathan Tha testified on Wednesday that he was aboard HMAS Larrakia, which arrived at the scene at about 4pm for the rescue mission.